Thermionic valve grids



United States Pate THERMIONIC VALVE GRIDS Clayton Arbuthnot Lane, llniield,V Frederick William James Strohm, Waltham Cross, and. Kenneth John Ellis, Ongar, England, assignors to Siemens Edison Swan Limited, London, England, a British company I-iledV Mar. 3:, 195,9, Ser. No. 79.6,922

Claims priority, application Great Britain Mar. 6, 1958 .81;Clams., (Cl;; 313x650).

This invention relates to the construction of thermionic' valve grids particularly for valves designed for very high frequency application.

The constructional rigidity of a conventional grid, that is one which consists of comparatively thick support wires with a continuous length of comparatively thin helix wire wound between them, is largely dependent on the total stiffness of the helix turns.

For certain applications of the radio valve, for instance for very high frequencies, the helix requires to be of very small diameter wire so that, in consequence, its total stiffness is insufficient to hold the support wires in correct relative position.

To overcome this it is necessary to construct `a rigid frame on which the thin helix Wire can be Wound and fixed to the frame.

I-t is an object of the present invention to provide a grid frame which is capable of supporting a thin helix wlre.

According to the present invention a thermionic valve grid comprises a plurality of metallic support rods held in spaced apart relationship to each other by metallic straps extending between the support rods and welded thereto to provide a rigid frame, at least one of the welded surfaces having a nickel coating, and a grid wire wound `in helical fashion around the frame.

By providing a nickel coating on at least one of the members welded together a more satisfactory weld can be obtained than with the direct welding of the metallic materials normally used for such components.

In order that the invention may be more fully understood reference may now @be made to the drawings accompanying this specification, in which:

Fig. 1 shows 1a grid in accordance with the invention;

Fig. 2 shows the method of constructing the support wires for the grid; -and Fig. 3 shows the process in which the support wires are strapped together.

Referring now to Fig. l the support rods of the grid are constructed of a metallic core 1 and a nickel sheath 2. Core 1 may consist of molybdenum or alternatively, steel. If steel is used instead of molybdenum there will be less rigidity for a given diameter of support rod or alternatively a larger diameter support rod for a given length will be required. Nickel sheath 2 may be a drawn tube or else formed as a lock or lap seam tube. The resultant composite rod whether with `a molybdenum or steel core has a greater mechanical strength than la solid nickel rod. Two molybdenum straps 3 and 3 are provided at each end of the support rods to hold the rods in spaced apart relationship and provide -a rigid frame for the helix wire 5. Straps 3 and 3' are each formed round the support rods and welded thereto as shown vat 4. Helix wire 5 may cornprise gold or silver plated tungsten which is wound on at about 60 percent to 80 percent of its breaking load. The gold or silver plating of the helix wire alloys with the nickel sheath 2 even when the temperature is below the eutectic of the two Imaterials thereby ensuring a good braze.

Th-e method by which the composite support rods are constructed is shown in Fig. 2. In the iigure 1a tool 6 is provided with a two-diameter hole into which `a molybdenum core 1 and a nickel sheath 2 each previously cut to the requisite length are inserted. A plate 7 then slides in the direction of arrow 9 to close. the entrance to this hole. A punch S is then driven in the direction of arrow 10 to force the rod into the tube `after which slide 7 is moved in the reverse `direction and the assembled composite support wire pushed out by further movement of punch 8.

The grid frame is then prepared on the combination tool shown in Fig. 3 which form the molybdenum straps round the support rods, welds them thereto, and finally shears off the completed frame in a successive series of operations on a continuous chain of grid frames.

ln more detail, ribbons of molybdenum 11 from which the straps are -formed vare pulled off spools (not shown) and preformed round an oversized rod 12. The preformed lengths of strap are then formed round the support rod 13 and mandril 14 by the closing of the two halves of the formed tool 15, mandril 14 having been previously pushed into position in a direction at right angles to the plane of the drawing. The arc over which each strap Iis in contact with the wires is arranged to extend from more than 90 so that the total arc of contact of both straps is greater than 180. Alternatively, the straps can be welded to the rods along `a line contact.

After forming the mandril 14 is withdrawn and the whole chain of frames is indexed to the right and welded by four electrodes 16 held in position in an insulating block 17. The indexing of the frames is carried out by means of a plunger 18 which enters the frame and then moves to the right to the dotted position shown pulling the whole chain of frames with it. At the final stage, each frame is cut off by cutters 19. A similar pair of straps is at the same time formed and welded at the other end of the support wires by means of similar forming and Welding tools to produce a rigid frame.

A -grid helix wire is now wound on to the frame under tension in any known manner. The turns of the wound grid wires are then brazed to the support -rods by the application of hot bars in close proximity to the support rods.

In an alternative arrangement nickel coated molybdenum straps land uncoated molybdenum or steel rods can be used. The nickel can be applied by `a plating process, a suitable thickness being 0:0005". If desired the support rods can be nickel plated instead of being inserted into a nickel sheath.

An advantage of using coated straps and uncoated rods is that when the rods and straps are stored on reels a strap when unwound Vfrom a reel will come oif virtually at, whereas a support rod wire requires to be straightened before use and in the straightening process any nickel plating is liable to be damaged.

What we claim is:

1. A thermionic valve grid comprising a plurality of metallic support rods, metallic straps extending between said support rods, welds between said straps and support rods holding said support rods in spaced lapart relationship to provide a rigid frame, a nickel coating covering at least one of said straps Iand rods at each weld, and a grid wire wound in helical fashion round the frame. l

2. A thermionic valve grid comprising a plurality of `support rods formed by the insertion of a metallic core into a nickel sheath, metallic straps -extending between saidv support rods, welds between said straps and support rods` Y holding said support rods in spaced apart relationship to 3 provide a rigid frame, and la grid wire wound in helical fashion round the frame.

3. A thermionic valve grid according to claim 2, in which said'metallic core consists of molybdenum.

4. A thermionic valve grid according to claim 3, in which said metallic straps consist of molybdenum.

5. A thermionic valve grid according to claim 2, in which said metallic core consists of steel.

6. A thermionic valve grid comprising a plurality of metallic support rods, metallic straps having a' nickel coating extending between the support rods, welds between said straps and said support rods holding said support rods in sp-aced apart relationship to provide a rigid frame, and a grid wire wound in helical fashion round the frame.

7. A thermionic valve grid comprising a plurality of metallic support rods, metallic straps extending between said support rods, welds between said straps and support rods extending round said support rods over an 'arc greater than 90 and holding said support rods in spaced apart relationship to provide a rigid frame, a nickel coating covering at least one of said straps and rods lat each weld, and a grid wire Wound in helical fashion round the frame.

8. A thermionic valve grid comprising a pair of metallic support rods, a pair of metallic straps extending between said support rods at one of their ends, a further pair of metallic straps extending between said support rods at the other of their ends, welds between said two pairs of straps and said support rods holding said support rods in parallel spaced apart relationship to provide a rigid frame, a nickel coating covering at least one of said straps and rods at each weld, and a grid wire wound in helical fashion round the frame.

References Cited in the le of this patent UNITED STATES PATENTS 2,845,691 Atherton et al Aug. 5, 1958 uff 5.3.4. 

